Sensores de gás e memoristores fabricados por oxidação anódica local utilizando Microscopia de Varredura por Sonda.

Abstract

In this work we have studied nano- and micro-scale metal oxide structures, which were directly fabricated onto a thin and microscopic metal track via scanning probe microscopy assisted local anodic oxidation (LAO). It is well known that some metal oxides are wide gap semiconductors, where oxygen vacancies act like n-type dopants. In particular, we have investigated the usage of metal-semiconductor-metalbarriers as gas sensors and memristors (memory-resistor). For the gas sensors, the active region of the devices were built by two distinct LAO routes, a slow (conventional) or a fast (unusual) one, which are employed to produce nano- and micro-sensors. Two distinct metal oxides, namely MoOx and TiOx, were tested at different temperatures using CO2 and H2 as test gases. Sensitivities down to ppm levels are demonstrated. Also, the influence of adsorbed water on these metal oxide conductivities was studied. Furthermore, the activation energy was evaluated and analyzed in the temperature range of this work. Thin metallic film and sensor stabilities and durability under the work atmospheres were also studied. The possibility of easy integration of the fast LAO route into microfabrication processes is also discussed. Memristive behavior naturally arises in metal-insulator-metal nanosystems. The observed switching processes in i-v curves can be explained in terms of movements of oxygen vacancies. Therefore, the coupled electron-ion dynamics are responsible for switching ON or OFF the device. In such nanostructures, the existence of a strong electric field when an external bias is applied between the metallic terminals is pointed out as the responsible for these movements. Here, the LAO technique was used tofabricate and study such structures. This process produces a metal-semiconductor-metal barrier, such as Ti-TiOx-Ti barriers, which, after an irreversible formation step, show the memristive behavior. In this new proposed manner, the barriers were built in a planar geometry, where SPM-based techniques can be implemented in situ during the device switching process. Hence, morphological studies of the barrier and the electrical characterization of the interface could be performed.